The present invention relates to a machine tool capable of driving a chiseling tool. A striker is accelerated directly by magnetic coils and strikes the tool. Machine tools of this type are known, for example, from U.S. Patent Application Publication No. US 2010/0206593.
The machine tool according to the invention has a tool holder which is set up to store a chiseling tool so that it can move along an axis of movement. A magneto-pneumatic striking mechanism has a primary actuator, which is arranged around the axis of movement, and sequentially includes a first magnetic coil and a second magnetic coil in the direction of impact. The striking mechanism is on the axis of movement within the magnetic coil, and in the direction of impact a striker and a die are sequentially arranged. Furthermore, the striking mechanism has an air spring which acts on the striker in the direction of the impact. The air spring may be wholly or partially within the first magnetic coil. The air spring has a ventilation opening which is open to the environment when the striker is at a distance of less than 10% of its stroke from the die, and otherwise the ventilation opening is closed. The ventilation opening is preferably the only opening of the pneumatic chamber forming the air spring to the environment. An exchange of air with the environment is therefore only possible when the striker is close to the die and the impact position. To determine the distance, the die is assumed to be in its home position. In the home position, the die is preferably opposite the direction of impact at a stop.
One embodiment provides that the ventilation opening of the air spring is arranged at the axial height of the end of the first magnetic coil pointing in the direction of impact. The ventilation opening is significantly closer to the end of the first magnetic coil pointing in the direction of impact than to the end pointing opposite the direction of impact. The striker may block the ventilation opening, for example, with its lateral surface. Specifically, when the striker advantageously overlaps with the first magnetic coil at every position.
One embodiment provides that a surface cross-section of the ventilation opening is designed such that with a pressure difference of 0.5 bar, at most 10% of the amount of air in the air spring flows through the ventilation opening in one second. The exchange of air through the ventilation opening is small. Ultimately, only losses in the air spring are supposed to be equalized, which emanate, for example, through leakage during the compression of the air spring. The ventilation opening can be realized by a single hole or a plurality of holes and/or slots located at approximately the same height.
One embodiment provides that the air spring is closed off by a stationary seal which is opposite to the direction of impact. The stationary seal is immobile with respect to the magnetic coil, the tool holder, etc. The pneumatic chamber of the pneumatic spring is insulated from the environment except for a ventilation opening. The ventilation opening is at the axial height of the end of the first magnetic coil facing the ring magnet.
One embodiment provides that a permanent and radially magnetized ring magnet is arranged between the first coil and the second coil. The ring magnet is composed, for example, of permanent magnets, with the respective same magnetic pole (N) of each facing of the axis of movement and with the other magnetic pole (S) facing away from the axis of movement. The ring magnet essentially generates a magnetic field which is permanently oriented to the axis movement and runs along the radial direction, and which runs in the opposite direction within the first magnetic coil and the second magnetic coil. This asymmetry can be used to set the magnetic field strength within the two coils in phase opposition to a high and a low value. The gradient of the magnetic field strength moves the striker based on the magnetic reluctance. The magnetic coils can be controlled by a controller in alternating phases. A magnetic field generated by the first magnetic coil within the first magnetic coil is super-positioned on the magnetic field of the ring magnet constructively in a first phase and destructively in a second phase. A second magnetic field generated by the second magnetic coil within the second magnetic coil is super-positioned on the magnetic field of the ring magnet destructively in the first phase and constructively in the second phase.
One embodiment provides that the die be of a soft magnetic material. The die extends into the second magnetic coil or into a yoke placed into the second coil in the direction of impact. The magnetizable die guides the magnetic field. The magnetic field generated by the second magnetic coil occurs substantially parallel to the direction of impact from the die, i.e., it is substantially perpendicular to the face of the die. The magnetic field generated by the ring magnet also occurs substantially perpendicular to the face of the die. This enables a high field strength near the face.